mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: White to colorless; Luster: Vitreous to pearly; Crystal Structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; SG: 2.71

Hardness: 3 on Mohs scale
Color: White to colorless
Luster: Vitreous to pearly

Identified July 5, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: White to colorless; Luster: Vitreous to pearly; Crystal Structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; SG: 2.71

Formation & geological history

Commonly forms in sedimentary environments through chemical precipitation or as a primary constituent of limestone and marble. Can also form in hydrothermal veins or as cave deposits (stalactites/stalagmites).

Uses & applications

Primary source of lime for cement and mortar, agricultural soil treatment, optical components (in clear rhombohedral form), and as a popular mineral specimen for collectors.

Geological facts

Calcite is famous for its double refraction (birefringence), where light passing through a clear specimen splits into two rays, causing objects seen through it to appear doubled. It will effervesce (fizz) vigorously when in contact with weak acid.

Field identification & locations

Identify in the field by its rhombohedral cleavage, softness (can be scratched by a copper penny), and the acid fizz test. Commonly found in limestone quarries and karst landscapes worldwide.